Legionnaires' disease, a pneumonia-like human infection caused by gram-negative bacteria of the genus Legionella, is virtually impossible to differentiate on a reliable clinical basis (involving assessment of patient symptoms without laboratory tests) from pneumonia and other similar lung infections. Because the disease may produce lung abscesses, infections in other bodily organs or bacteremia, and its mortality rate is significantly increased by delay in commencing appropriate therapy, there is a need for rapid and reliable diagnostic tests which has to date been only partially met. Stout, J. E. and Yu, V. L., “Legionellosis”, 337, N. Eng. J. Med. 682-687 (1997). Efforts to develop such tests have been hampered by the fact that there are a number of Legionella species, at least some of which are known to have a number of distinct serogroups.
Legionnaires' disease was first recognized in the summer of 1976 and a number of techniques for detecting Legionella (“L.”) pneumophila, which is now known to account for some 90% of cases (Stout and Yu, supra), have been developed in the interim. In general, these tests are time-consuming and incapable of identifying more than one serogroup of the 15 serogroups known so far to fall within the L. pneumophila species. It should be noted, however, that, as reported by Stout and Yu, supra, more than 80% of reported cases of Legionnaires' disease are attributable to L. pneumophila serogroup 1—a fact which makes the development of a rapid, reliable immunoassay for that entity of particular importance and has led researchers to focus on this as a priority.
The early efforts to establish the identity of the causative agent of Legionnaires' disease depended largely upon culturing the bacteria for 5 to 6 days and examining the culture microscopically. Efforts to speed up the identification process led to numerous immunochemical tests of varying sensitivity and specificity including, inter alia, the presently commercially available EQUATE™ radioimmunoassay (“RIA”), and the Binax enzyme immunoassay (“EIA”), both of which are sold in kit form by applicants' assignee, Binax, Inc. As indicated by Hackman, B. A. et al. in “Comparison of Binax Legionella Urinary Antigen EIA Kit with Binax RIA Urinary Antigen Kit for Detection of Legionella pneumophila Serogroup I Antigen”, 34 J. Clin. Microbiol. 1579-1580 (1996), both of these assays were found to be specific for L. pneumophila Serogroup I antigen. The reported sensitivity of the EIA was 77%; that of the RIA was higher. The article indicates that each can be performed within “less than 3 h[ours] from beginning to end”; in Binax's own tests each requires at least 2½ hours to perform. More information about this EIA assay appears in Kazandjian, D. et al., “Rapid Diagnosis of Legionella pneumophila Serogroup I Infection with Binax Enzyme Immunoassay Urinary Antigen Test”, 35 J. Clin. Immunobiol. 954-956 (1997).